DESCRIPTION: (from applicant's abstract) The importance of studying synaptic function at the molecular level is most obvious for understanding mental and neurological diseases where psychopharmacological therapeutics, modern molecular genetics and biochemically-oriented neurophysiology indicate an underlying synaptic malady. Long-term presynaptic facilitation (LTF) of sensory-to-motor neuron synapses, which is a form of plasticity underlying behavioral sensitization in the marine mollusk Aplysia and an elementary form of learning, can be produced by the action of the cAMP-dependent protein kinase (PKA). Ubiquitin-proteasome-mediated degradation of PKA regulatory R-subunits occurs in sensory neurons when treated to produce long-term facilitation; this molecular change endures only if new protein is made. No change in catalytic (C) subunits occurs. A decreased R/C ratio produces a kinase that is more sensitive to subsaturating cAMP and sets the baseline extent of protein phosphorylation within the neuron at a higher level for at least 24h. The fine control of cAMP-dependent phosphorylation is mediated by regulated proteolysis through the ubiquitin-proteasome pathway, which degrades R subunits selectively. This pathway is up-regulated by the induction of the immediate early gene Ap -ubiquitin C terminal hydrolase, which enhances proteolysis by the proteasome. Our first aim is to identify the coupling and ligating enzymes (E2 and E3) that specifically ubiquitinate R subunits and to determine whether they are induced during LTF. Why does PKA remain persistently active long after LTF has been induced? Evidence suggests the regulation of protein synthesis locally at synapses. We will test the idea that the persistent kinase is required to produce proteins needed for augumented translation as well as cytoskeletal proteins for the growth of new synapses.